All the code changed, so it's not surprising old code will not work in more recent versions.

As a heads up, you could use : Tools > Developer Tools > select 'Developer Toolbox' You will get a pop up window asking you to 'OK' connection - often it hides behind a window.

/* Change background color for read messages in Thread Pane*/
#threadTree tbody [data-properties~="read"] {
background-color: #f1f715 !important;  
color: #6564cf !important; 
 }

Thanks a lot for the code! Just to clarify, where exactly would I copy / paste it? Not sure where to paste it once I open the developper tools... (I tried the userChrome file with no success). Thanks, ulrike

Thanks a lot for the code! Just to clarify, where exactly would I copy / paste it? Not sure where to paste it once I open the developper tools... (I tried the userChrome file with no success). Thanks, ulrike

Sorry, I was under the impression you understood all about 'userChrome.css' files and just needed to know what part needed a fix.

The 'Developer Tools is just way of allowing you to see the code behind the new design.

I'm not sure if you have created a 'chrome' folder in correct location and I'm not sure if you have created a correct 'userChrome.css' file, so I'm starting from scratch and offering full info.

1. Please check in Thunderbird to see if a setting needs switching on.

• Settings > General
• Scroll to bottom and click on 'Config Editor' button
• In search type : legacy
• look for this line: toolkit.legacyUserProfileCustomizations.stylesheets
• If it is set as 'false' :
• click on the far right arrow type icon to toggle from 'false' to say 'TRUE'

2. Now to locate the profile name folder: In Thunderbird

• Help > Troubleshooting Information
• in 'Application Basics' - half way down is 'Profile Folders' - click on 'Open Folder'

A new window opens the current profile name folder - showing the contents.

• Exit Thunderbird now. This is important.

I'm going to give the full instructions because I do not know if people already know how to create and use a userChrome.css file.

3. Create the chrome folder

• In the 'profile name' folder (you should be already in that location) create a new folder and call it 'chrome'. The spelling is important - note it is all lower case - see image below as a guide to where it should be placed.

4. Now to create the 'userChrome.css' file - but if you already have done this - either delete your initial attempt and start again as per instructions below OR open it using Notepad. Otherwise...

• Open a simple text editor program such as 'Notepad'.
• Copy all the text between the lines below and paste it into 'Notepad'.

If editing a 'userChrome.css' file Where it says: treechildren::-moz-tree-row(read)' - you need to alter that line, so it says #threadTree tbody [data-properties~="read"] Or just remove that section and copy paste in the section I mentioned.

/* Change background color for 'read' messages in Thread Pane*/
#threadTree tbody [data-properties~="read"] {
background-color: #f1f715 !important;  
color: #6564cf !important; 
 }

• Save the file as 'userChrome.css' - note the spelling of this is important - all lower case except the C.
• Save it in the 'chrome' folder. - see attached image as guide.

Check that file really is called 'userChrome.css' and not 'userChrome.css.txt' - it has to be saved as a Cascading Style Sheet (css) and not a text document. So if you see 'userChrome.css.txt' - no problem - just rename it by removing the .txt - you will get ask are you sure as it may effect things - just say yes because you really do want to do it. - see image below which shows the 'Type' as CSS.

Start Thunderbird